1. Field of the Invention
The present invention relates generally to multi-chip modules including semiconductor devices in stacked arrangement and, more specifically, to stacked multi-chip modules including at least one semiconductor device that is superimposed over contact areas on a substrate over which an underlying semiconductor device is not superimposed, with one of the stacked semiconductor devices being electrically connected to the contact areas. The present invention also relates to substrates for use in multi-chip modules that include stacked semiconductor devices, which substrates include contact areas located between the outer peripheries of regions over which semiconductor devices are to be positioned in adjacent, stacked arrangement.
2. Background of Related Art
In order to conserve the amount of surface area, or “real estate,” consumed on a carrier substrate, such as a circuit board, by semiconductor devices connected thereto, various types of increased density packages have been developed. Among these various types of packages is the so-called “multi-chip module” (MCM). Some types of multi-chip modules include assemblies of semiconductor devices that are stacked one on top of another. The amount of surface area on a carrier substrate that may be saved by stacking semiconductor devices is readily apparent. A stack of semiconductor devices consumes roughly the same amount of real estate on a carrier substrate as a single, horizontally oriented semiconductor device or semiconductor device package.
Due to the disparity in processes that are used to form different types of semiconductor devices (e.g., the number and order of various process steps), the incorporation of different types of functionality into a single semiconductor device has proven very difficult to actually reduce to practice. Even in cases where semiconductor devices that carry out multiple functions can be fabricated, multi-chip modules that include semiconductor devices with differing functions (e.g., memory, processing capabilities, etc.) are often much more desirable since the separate semiconductor devices may be fabricated independently and later assembled with one another much more quickly and cost-effectively (e.g., lower production costs due to higher volumes and lower failure rates).
Multi-chip modules may also contain a number of semiconductor devices that perform the same function, effectively combining the functionality of all of the semiconductor devices thereof into a single package.
An example of a conventional, stacked multi-chip module includes a carrier substrate, a first, larger semiconductor device secured to the carrier substrate, and a second, smaller semiconductor device positioned over and secured to the first semiconductor device. Any suitable adhesive may be used to secure the semiconductor devices to one another. The second semiconductor device does not overlie bond pads of the first semiconductor device and, thus, the second semiconductor device does not cover bond wires that electrically connect bond pads of the first semiconductor device to corresponding contacts or terminal pads of the carrier substrate. To facilitate the connection of bond wires between bond pads and their corresponding contact pads, each of the contact pads of the carrier substrate is positioned beyond an outer periphery of the lowermost of the stacked semiconductor devices. Such a multi-chip module is disclosed and illustrated in U.S. Pat. No. 6,212,767, issued to Tandy on Apr. 10, 2001 (hereinafter “the '767 Patent”).
U.S. Pat. No. 5,323,060, issued to Fogal et al. on Jun. 21, 1994 (hereinafter “the '060 Patent”) shows one example where dice of the same size are stacked on top of one another over a circuit board. Bonding wires are connected from the bond pads of each die to corresponding terminal pads on the circuit board. Each of the terminal pads is located beyond the outer peripheries of the stacked dice.
Stacked multi-chip modules of other configurations have also been developed. For example, it is known that stacked multi-chip modules may include large semiconductor devices positioned over smaller semiconductor devices and that adjacent semiconductor devices may be staggered relative to one another or have different orientations.
Different electrical connection technologies, including wire bonding, tape-automated bonding (“TAB”), and controlled-collapse chip connection (“C-4”), which results in a so-called flip-chip arrangement, are but a few of the ways in which discrete conductive elements may be formed in stacked multi-chip modules. Different electrical connection technologies have also been used in single multi-chip modules, with the bond pads of one semiconductor device being electrically connected to corresponding contact areas of a substrate of the multi-chip module with a different type of discrete conductive element than that used to form electrical connections between the bond pads of another semiconductor device and their corresponding contact areas of the substrate.
Stacked multi-chip modules in which bond pads of the semiconductor devices are electrically connected to corresponding contact areas of a substrate by way of discrete conductive elements that extend laterally over a periphery of the semiconductor device to which they are connected, such as bond wires or conductive TAB elements carried upon a dielectric film, typically include substrates with contact areas that are positioned outside the peripheries of all of the stacked semiconductor devices thereof. To avoid routing congestion of the contact areas and terminals, the substrates of such stacked multi-chip modules must be routed using advance layout rules. Due to the amount of surface area, or “real estate” of the substrate consumed by these contact areas and their corresponding conductive traces, the size of the substrate may be undesirably large, extending well beyond the outer periphery of the largest semiconductor device thereof. The inability to reduce the minimum area around the outer periphery of the largest die of a stacked multi-chip module prevents the design and manufacture of multi-chip modules of ever-decreasing dimensions.
When flip-chip type connections are used to connect a semiconductor device of a stacked multi-chip module to either another semiconductor device of the multi-chip module or the substrate thereof, the bond pads of at least one of the other semiconductor devices of the multi-chip module are typically connected to corresponding contact areas of the substrate by way of laterally extending discrete conductive elements. Consequently, at least some of the contact areas of the substrate must be located beyond an outer periphery of the semiconductor device that includes bond pads that correspond to these contact areas. As a result, a considerable amount of the real estate of such a substrate does not carry the contact areas or conductive elements that correspond to the bond pads of the semiconductor devices, making the substrate undesirably large.
Accordingly, there are needs in the art for substrates for use in stacked multi-chip modules and having smaller dimensions and for stacked semiconductor device assemblies that include such compact substrates.